Question: If $a + b + c = -1$ and $x + y + z = -6$, what is $-9z - 9x + 10a - 9y + 10b + 10c$ ?
Answer: $= 10a + 10b + 10c - 9x - 9y - 9z$ $= (10) \cdot (a + b + c) + (-9) \cdot (x + y + z)$ $= (10) \cdot (-1) + (-9) \cdot (-6)$ $= -10 + 54$ $= 44$